Dielectric ceramic, method of producing the same, and monolithic ceramic capacitor

ABSTRACT

A dielectric ceramic includes, in composition, a perovskite-type compound having the general formula ABO 3  containing Ba, Ca and Ti, and an additive component containing Si, R(La or the like), and M (Mn or the like), the additive component not being solid-dissolved and, moreover, the major component existing in at least 90% of the cross-section of each of the crystal grains of which the number is equal to at least 85% of that of all of the crystal grains contained in the dielectric ceramic, at least the Ba, the Ca, the Ti, the Si, the R, and the M being contained at at least 85% of the analytical points in the crystal grain boundaries of the dielectric ceramic.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a dielectric ceramic, a methodof procuring the same, and a monolithic ceramic capacitor containing thedielectric ceramic and, particularly, to the improved reduction of thethickness of a dielectric ceramic layer contained in the monolithicceramic capacitor which can be advantageously carried out.

[0003] 2. Description of the Related Art

[0004] In general, monolithic ceramic capacitors are produced asfollows.

[0005] First, a ceramic green sheet is prepared. The green sheetcontains a dielectric ceramic raw material and has an electroconductivematerial for an internal electrode applied to the surface of the greensheet in a desired pattern. For example, a dielectric ceramic containingBaTiO₃ as a major component is used.

[0006] Subsequently, plural ceramic green sheets each having theelectroconductive material applied thereon are laminated andhot-press-bonded. Thus, an integrated green laminate is prepared.

[0007] Next, the integrated green laminate is fired. Thus, a sinteredlaminate is produced. The laminate is provided with the internalelectrodes formed inside the laminate, which are made from theabove-described electroconductive material.

[0008] Then, an external electrode is formed on the outer surface of thelaminate so as to be electrically connected to a specified internalelectrode. In particular, the external electrode is formed, e.g., byapplying electroconductive paste containing electroconductive metalpowder and glass frit to the outer surface of the laminate, and firing.

[0009] Thus, a monolithic ceramic capacitor is produced.

[0010] Referring to the electroconductive material to form the internalelectrode, base metals such as nickel, copper, or the like, which arerelatively inexpensive, have been used in many cases in recent years.However, to produce a monolithic ceramic capacitor containing aninternal electrode made of a base metal, firing in a neutral or reducingatmosphere is required to prevent the base metal from being oxidizedduring firing. Therefore, the dielectric ceramic contained in themonolithic ceramic capacitor must have a reduction-proof property.

[0011] As a dielectric ceramic which has the above-described resistanceto reduction and can form a monolithic ceramic capacitor of which thecapacitance—temperature characteristic meets the requirement ofCharacteristic B of JIS standard, a material containing BaTiO₃ as amajor component, and oxides of rare earth elements, oxides of Mn, Fe,Ni, Cu or the like, a sintering-assisting agent, and so forth are usedas additives.

[0012] Referring to the above-described dielectric ceramic, for example,Japanese Unexamined Patent Application Publication No. 5-9066 (PatentDocument 1), Japanese Unexamined Patent Application Publication No.9-270366 (Patent Document 2), Japanese Unexamined Patent ApplicationPublication No. 11-302071 (Patent Document 3), and Japanese UnexaminedPatent Application Publication No. 2000-58377 (Patent Document 4)propose the compositions of dielectric ceramics which have a highdielectric constant, a lower temperature-dependent change of adielectric constant, and a long high-temperature load service life,respectively.

[0013] Referring to the structure of the dielectric ceramic, JapaneseUnexamined Patent Application Publication No. 6-5460 (Patent Document5), Japanese Unexamined Patent Application Publication No. 2001-220224(Patent Document 6), and Japanese Unexamined Patent ApplicationPublication No. 2001-230149 (Patent Document 7) propose dielectricceramics having a so-called core-shell structure.

[0014] Moreover, Japanese Unexamined Patent Application Publication No.2001-313225 (Patent Document 8) proposes a dielectric ceramic having aso-called core-shell structure in which the core is partially exposedfrom the shell.

[0015] Recently, electronics have been remarkably developed, andsimultaneously, the sizes of electronic parts have been rapidlydecreased. Moreover, monolithic ceramic capacitors have experienced atrend toward reduction of the size and increase of the capacitance. Asregards effective means for realizing small-sizes and large capacitancesin monolithic ceramic capacitors, the thickness of a dielectric ceramiclayer is reduced, for example. In general, the thicknesses of dielectricceramic layers contained in such commercially available products are upto about 2 μm. The thicknesses of dielectric ceramics investigated inlaboratories are up to about 1 μm. Enhancement of the dielectricconstants of dielectric ceramics is important for realizing small-sizesand large capacitances of the dielectric ceramics.

[0016] Moreover, an electrical circuit must be operated with highstability, irrespective of variations in temperature. For this purpose,capacitors used in the electrical circuit must be stable against thevariation of temperature.

[0017] As seen in the above-description, the advent of monolithicceramic capacitors, of which the temperature-dependent change of thecapacity is small, the electrical insulating property is high and thereliability is superior, even if the thickness of a dielectric ceramiclayer is reduced, is earnestly desired.

[0018] The dielectric ceramic described in Patent Document 1 meets thecharacteristic X7R specified in EIA Standard, and moreover, exhibits ahigh electrical insulating property. However, when the thickness of adielectric ceramic layer is reduced, and specifically in the case inwhich the thickness is less than 5 μm, especially less than 3 μm, thecapacitance-temperature characteristic and the reliability of thedielectric ceramic do not sufficiently meet the demands in the market.

[0019] Similarly, the dielectric ceramics described in Patent Documents2, 3, and 4, are such that the smaller the thickness of a dielectricceramic layer is to be, e.g., less than 2 μm, the more thecapacitance-temperature characteristics and the reliabilities aredeteriorated.

[0020] Moreover, each of the so-called core-shell type dielectricceramics described in Patent Documents 5, 6, and 7 comprises a coreportion having a ferroelectric property and a shell portion having aparaelectric property. This dielectric ceramic has a superiorcapacitance—temperature characteristic. However, the shell portion has alow dielectric constant. Thus, the dielectric constant of the wholedielectric ceramic is reduced, due to the existence of the shellportion. The reason is that when plural dielectrics exist in a ceramic,the dielectric constant of the overall dielectric ceramic issubstantially equal to a value calculated by addition of the logarithmsof the dielectric constants according to the so-called logarithmicmixing rule. Moreover, problems occur in that with the thickness of adielectric ceramic layer being reduced, the capacitance—temperaturecharacteristic is deteriorated, and also, the reliability is reduced.

[0021] For to the dielectric ceramic having a structure described inPatent Document 8, control of construction is carried out using thefiring temperature. Therefore, the electrical characteristics of thedielectric ceramic tend to be dispersed. Thus, problems occur in thatfor a dielectric ceramic layer of which the thickness is reduced, thecapacitance—temperature characteristic and the reliability can not beensured.

[0022] As seen in the above-description, if the thickness of adielectric ceramic layer is reduced so that the size of a monolithicceramic capacitor can be reduced, the capacitance thereof is increased,and also, the level of an AC signal is maintained at the same value asthat before the reduction of the thickness, the electric field strengthapplied per dielectric ceramic layer is increased, and thus, thecapacitance—temperature characteristic is remarkably deteriorated.Moreover, if the thickness of a dielectric ceramic layer is decreasedand the DC rated voltage is set at the same value as that before thereduction of the thickness, the electric field strength applied perdielectric ceramic layer is increased, and thus, the reliability isremarkably deteriorated.

[0023] Accordingly, the advent of a dielectric ceramic which has a highdielectric constant is desired, which can be used to form a dielectricceramic layer of which the temperature-dependent dielectric constant isnot deteriorated, even if the thickness of the layer is reduced, andwhich can provide a monolithic ceramic capacitor with a highreliability.

SUMMARY OF THE INVENTION

[0024] It is an object of the present invention to provide a dielectricceramic, a method of producing the dielectric ceramic which can satisfythe above-described requirements, and a monolithic ceramic capacitorformed using the dielectric ceramic.

[0025] According to the present invention, there is provided adielectric ceramic which includes, in composition, a perovskite-typecompound having the general formula ABO₃ in which A represents Ba andCa, or Ba, Ca and Sr, and B represents Ti or Ti and at least one of Zrand Hf which is substituted for a part of the Ti, and an additivecomponent containing Si, R and M, in which R represents at least one ofLa, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, and Mrepresents Mn, Ni, Co, Fe, Cr, Cu, Mg, Al, V, Mo and W, the dielectricceramic having crystal grains and crystal grain boundaries between thecrystal grains, the additive component not being solid-dissolved and,moreover, the major component existing in at least about 90% of thecross-section of each of the crystal grains of at least about 85% of allof the crystal grains, and at least the Ba, Ca, Ti, Si, R and M being atat least about 85% of the analytical points in the crystal grainboundaries. Even if the thickness of a dielectric ceramic layer formedof the dielectric ceramic is reduced, the dielectric ceramic layer has ahigh reliability. Also, the capacitance—temperature characteristic issuperior and the dielectric constant is high. Accordingly, a monolithicceramic capacitor having a high reliability and a superiorcapacitance—temperature characteristic can be realized by forming thedielectric ceramic layers of a monolithic ceramic capacitor by using thedielectric ceramic. In addition, the size of the monolithic ceramiccapacitor can be reduced, and the capacitance thereof is increased, dueto the reduction of the thickness of the dielectric ceramic layer.

[0026] It is to be noted that whether the additive component issolid-dissolved in at least 90% of the cross-section of a particularcrystal grain or not is determined based on the TEM analysis with adetection lower limit of 0.5%.

[0027] In this patent specification, the expression “crystal grainboundary” means an area defined by two crystal grains and also, an areadefined by at least three crystal grains(the so-called triple point).More specifically, if a distinct layer is crystallographically observedbetween crystal grains in the cross-section of a ceramic, the layer isdefined as a crystal grain boundary. On the other hand, if no layer iscrystallographically observed between crystal grains in thecross-section of a ceramic, and crystal grains are joined with eachother, an area extended over a width of 2 nm on both of the sides of thejoining line as a center line, including the joining point, is definedas a crystal grain boundary.

[0028] Preferably, the formula Ca_(g)/Ti_(g)<Ca_(b)/Ti_(b) isestablished in the dielectric ceramic of the present invention, in whichCa_(g) is the amount of Ca, and Ti_(g) is the amount of Ti contained inthe crystal grains, and Ca_(b) is the amount of Ca, and Ti_(b) is theamount of Ti contained in the crystal grain boundaries. Thereby, thereliability can be more enhanced.

[0029] Also, preferably, the concentration of Ca in the crystal grainsis in the range of about 1 to 20 molar percent based on the amount ofthe element A contained in the, major component ABO₃. Thereby, thedielectric ceramic has a high dielectric constant.

[0030] Preferably, the concentrations on an element basis of the R andthe M in the additive component are in the ranges of about 0.05 to 1.5moles and about 0.1 to 2 moles, respectively, based on 100 moles of themajor component. Thereby, the dielectric constant, thecapacitance—temperature characteristic, and the reliability can befurther enhanced.

[0031] Moreover, there is provided according to the present invention amethod of producing a dielectric ceramic which includes the steps of:synthesizing a perovskite-type compound having the general formula ABO₃in which A represents Ba and Ca, or Ba, Ca and Sr, and B represents Tior Ti and at least one of Zr and Hf which is substituted for a part ofthe Ti, the perovskite-type compound having a crystallographic axialratio c/a of at least about 1.009; calcining compounds containing atleast Ba, Ca, Ti, Si, R and M, in which R is at least one of La, Ce, Pr,Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, and M represents atleast one of Mn, Ni, Co, Fe, Cr, Cu, Mg, Al, V, Mo and W to produce acalcined material; and firing a compounded material, as a raw materialfor the dielectric ceramic, containing a mixture of the perovskite-typecompound and the calcined material. Thus, the above-described dielectricceramic can be produced easily and securely.

[0032] Since the crystallographic axial ratio c/a is at least about1.009, the synthesis degree is sufficiently high. Thus, the majorcomponent of the perovskite-type compound and the additive component canbe inhibited from reacting with each other. Thus, the dielectric ceramicof the present invention can be produced.

[0033] Preferably, the mole ratio Ca/Ti of the perovskite-type compoundobtained in the step of synthesizing the perovskite-type compound issmaller than the mole ratio Ca/Ti in the calcined material obtained inthe step of producing the calcined material. Thereby, theabove-described formula Ca_(g)/Ti_(g)<Ca_(b)/Ti_(b) can be established,in which Ca_(g) is the amount of Ca, and Ti_(g) is the amount of Ticontained in the crystal grains, and Ca_(b) is the amount of Ca, andTi_(b) is the amount of Ti contained in the crystal grain boundaries.

[0034] Moreover, there is provided a monolithic ceramic capacitoraccording to the present invention which includes: a laminate whichcontains plural laminated dielectric ceramic layers and plural internalelectrodes extended along particular interfaces between the pluraldielectric ceramic layers and overlapping each other in the laminationdirection; and external electrodes formed on the outer surface of thelaminate so as to be electrically connected to predetermined ones of theinternal electrodes; the dielectric ceramic layers being made of theabove-described dielectric ceramic.

[0035] The dielectric ceramic of the present invention can be fired in areducing atmosphere. In the case in which the monolithic ceramiccapacitor is formed using the dielectric ceramic, a base metal can beadvantageously used as an internal electrode material. Moreover, in thecase in which the dielectric ceramic layers and the external electrodesare simultaneously fired, a base metal can be advantageously used as anexternal electrode material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a cross-sectional view illustrating a monolithic ceramiccapacitor 1 according to an embodiment of the present invention;

[0037]FIG. 2 is a graph showing the analytical results of thecomposition inside of a crystal grain contained a sample 1 which is anexample of the present invention, determined by TEM-EDX; and

[0038]FIG. 3 is a graph showing the analytical results of thecomposition in a crystal grain boundary of the sample 1 illustrated inFIG. 2, determined by TEM-EDX.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039]FIG. 1 is a cross-sectional view illustrating a monolithic ceramiccapacitor 1 according to an embodiment of the present invention.

[0040] The monolithic ceramic capacitor 1 contains a laminate 2. Thelaminate 2 comprises plural dielectric ceramic layers 3 laminated toeach other, and plural internal electrodes 4 and 5 formed at theinterfaces between the plural dielectric ceramic layers 3, respectively.The internal electrodes 4 and 5 are formed so as to reach the outersurfaces of the laminate 2. The internal electrodes 4 extended to one 6of the end faces of the laminate 2 and the internal electrodes 5extended to the other end face 7 are alternately arranged inside thelaminate 2.

[0041] External electrodes 8 and 9 are formed by applying anelectroconductive paste to the end-faces 6 and 7 of the surface of thelaminate 2, and baking the paste. First plating layer 10 and 11 areformed on the external electrodes 8 and 9, and then, second platinglayers 12 and 13 are formed thereon, if necessary.

[0042] In the monolithic ceramic capacitor 1, the plural internalelectrodes 4 and 5 are formed so as to overlap each other in thelamination direction of the laminate 2. Thereby, electrostaticcapacitances are generated between neighboring internal electrodes 4 and5. Moreover, the internal electrodes 4 are electrically connected to theexternal electrodes 8, and the internal electrodes 5 are electricallyconnected to the external electrodes 9, respectively. Thereby, theabove-described static capacitances are drawn via the externalelectrodes 8 and 9.

[0043] The dielectric ceramic layer 3 is formed of the followingdielectric ceramic according to the present invention to be incomposition, a perovskite-type compound having the general formula ABO₃,as a major component, in which A represents Ba and Ca, or Ba, Ca, andSr, and B represents Ti, or Ti and at least one of Zr and Hf which issubstituted for a part of the Ti, and an additive component containingSi, R and M, in which R represents at least one of La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, and M represents Mn, Ni, Co,Fe, Cr, Cu, Mg, Al, V, Mo and W, the dielectric ceramic having crystalgrains and crystal grain boundaries between the crystal grains, theadditive component not being solid-dissolved and, moreover, the majorcomponent existing in at least about 90% of the cross-section of each ofthe crystal grains of at least about 85% by number are of all of thecrystal grains, is such that at least the Ba, Ca, Ti, Si, R, and M arecontained at at least about 85% of the analytical points in the crystalgrain boundaries.

[0044] If the dielectric ceramic does not meet the above-describedrequirements, inconveniently, the dielectric constant of the dielectricceramic is low, the capacitance—temperature characteristic isdeteriorated and the high temperature load service life becomes short.

[0045] Preferably, the formula Ca_(g)/Ti_(g)<Ca_(b)/Ti_(b) isestablished in the dielectric ceramic, in which Ca_(g) is the amount ofCa, and Ti_(g) is the amount of Ti contained in the crystal grains, andCa_(b) is the amount of Ca, and Ti_(b) is the amount of Ti contained inthe crystal grain boundaries.

[0046] By satisfying the above-described requirement, the hightemperature load service life is further prolonged, and the reliabilitycan be further enhanced.

[0047] Preferably, the concentration of Ca in the crystal grains in thedielectric ceramic is in the range of about 1 to 20 molar percent basedon the amount of the element A contained in the major component ABO₃.Thereby, the dielectric constant can be further increased.

[0048] Preferably, the concentrations on an element basis of the R andthe M in the additive component in the dielectric ceramic are in theranges of about 0.05 to 1.5 moles and about 0.1 to 2 moles, based on 100moles of the major component, respectively. Thereby, the dielectricconstant is further increased, the capacitance—temperaturecharacteristic is further enhanced and the high temperature load servicelife is prolonged.

[0049] Hereinafter, a method of producing the dielectric ceramic or themonolithic ceramic capacitor shown in FIG. 1 will be described.

[0050] First, a powder raw material for the dielectric ceramic to formthe dielectric ceramic layer is prepared. Preferably, the powdery rawmaterial is produced as follows.

[0051] As the A of the general formula ABO₃, Ba and Ca, or Ba, Ca, andSr is selected, and as the B, Ti, or Ti and at least one of Zr and Hfwhich is substituted for a part of the Ti is selected. Moreover, thecontents of the A and the B are selected. Thus, the perovskite-typecompound ABO₃ is synthesized. In this case, it is important that theperovskite-type compound has a crystallographic axial ratio c/a of atleast 1.0090. That is, it is important to enhance the synthetic degreeor the crystallinity.

[0052] On the other hand, compounds containing at least Ba, Ca, Ti, Si,R and M, in which R is at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, Lu and Y, and M represents at least one of Mn, Ni,Co, Fe, Cr, Cu, Mg, Al, V, Mo and W are calcined to produce a calcinedmaterial.

[0053] Subsequently, the perovskite-type compound and the calcinedmaterial are mixed with each other. The obtained compounded material isused as the powdery raw material.

[0054] Since the powdery raw material is produced as described above,the dielectric ceramic satisfying the above-described requirement can beeasily produced. Moreover, the dielectric ceramic satisfying theabove-described requirement also can be produced by adjustment of thefiring conditions, in addition to using the above-described process ofproducing the powdery raw material.

[0055] The Ca/Ti mole ratio of the perovskite-type compound is set to besmaller than the mole ratio Ca/Ti in the calcined material. Thereby, thedielectric ceramic having the formula Ca_(g)/Ti_(g)<Ca_(b)/Ti_(b), inwhich Ca_(g) is the amount of Ca, and Ti_(g) is the amount of Ticontained in the crystal grains, and Ca_(b) is the amount of Ca, andTi_(b) is the amount of Ti contained in the crystal grain boundaries, asdescribed above, can be produced.

[0056] Moreover, the amount of Ca in the perovskite-type compound andthe average grain size can be adjusted by controlling the synthesisconditions for the perovskite-type compound.

[0057] Then, an organic binder and a solvent are added to and mixed withthe powdery raw material for the dielectric ceramic produced asdescribed above, to form slurry. A ceramic green sheet, which is to be adielectric ceramic layer 3, is formed by use of the slurry.

[0058] Thereafter, electroconductive paste films, which are to beinternal electrodes 4 and 5, are formed on particular ceramic greensheets by screen-printing. The electroconductive paste films contain abase metal such as nickel, a nickel alloy, copper or a copper alloy asan electroconductive component. The internal electrodes 4 and 5 may beformed, e.g., by evaporation, plating, or the like, not only by thescreen-printing.

[0059] Thereafter, plural ceramic green sheets each having anelectroconductive paste film formed thereon as described above arelaminated to each other. Then, ceramic green sheets each having noelectroconductive paste film formed thereon are laminated in such amanner that the above-described ceramic green sheets are sandwichedbetween them. These ceramic green sheets are press-bonded, and are cut,if necessary. Thus, a green laminate, which is to be a laminate 2, isproduced. The ends of the electroconductive paste films are exposed ontothe end-faces of the green laminate.

[0060] Subsequently, the green laminate is fired in a reducingatmosphere. Thereby, the laminate 2 after the sintering, as shown inFIG. 1, is obtained. In the laminate 2, the ceramic green sheets formdielectric ceramic layers 3, and the electroconductive paste films formthe internal electrodes 4 and 5.

[0061] External electrodes 8 and 9 are formed on the end-faces 6 and 7of the laminate 2 so as to be electrically connected to the exposed endsof the internal electrodes 4 and 5, respectively.

[0062] Materials for the external electrodes 8 and 9 may be the same asthose for the internal electrodes 4 and 5. Silver, palladium,silver-palladium alloys or the like, may be used. Glass frits ofB₂O₃—SiO₂—BaO type glass, B₂O₃—Li₂O—SiO₂—BaO type glass or the like maybe added to the powders of the above-described metals. Appropriatematerials are selected considering uses of the monolithic ceramiccapacitor and the places it will be used.

[0063] For formation of the external electrodes 8 and 9, ordinarily, apaste containing the above described metal powders is applied to theouter surface of the fired laminate 2 and is baked. The paste may beapplied to the outer surface of the green laminate before the firing,and is simultaneously fired and baked with the green laminate to providethe laminate 2.

[0064] Thereafter, the external electrodes 8 and 9 are plated withnickel, copper or the like. Thus, first plating layers 10 and 11 areformed. Then, the first plating layers 10 and 11 are plated with solder,tin or the like. Thus, second plating layers 12 and 13 are formed. Theformation of the plating layers 10 to 13 on the external electrodes 8and 9 may be omitted, depending on the intended uses of the monolithicceramic capacitor 1.

[0065] As described above, the monolithic ceramic capacitor 1 isproduced.

[0066] There is a possibility that Al, Sr, Zr, Fe, Hf, Na, Co, W, Mo, Mnor the like is present as impurities in the process of preparing apowdery raw material for the dielectric ceramic, and in other productionprocesses. These impurities have a possibility of existing inside thecrystal grains and at crystal grain boundaries. However, the presence ofthese impurities does not become a problem with the electricalcharacteristics of the monolithic ceramic capacitor.

[0067] Preferably, nickel or copper is used as a material for theinternal electrodes 4 and 5. In this case, components contained in theinternal electrodes 4 and 5 have a possibility of being diffused to bein the crystal grains or in the crystal grain boundaries of thedielectric ceramic during the firing process for production of themonolithic ceramic capacitor 1. This is not a problem with theelectrical characteristics of the monolithic ceramic capacitor 1.

[0068] Hereinafter, experimental examples will be described, which werecarried out to identify the advantages of the present invention.

EXPERIMENTAL EXAMPLES EXPERIMENTAL EXAMPLE 1

[0069] In Experimental Example 1, (Ba_(0.95)Ca_(0.05))TiO₃ was used asmajor component having the general formula ABO₃, which contains Ba, Caand Ti. As additive components, BaCO₃, CaCO₃, TiO₂, SiO₂, Dy₂O₃ and NiOwere used, as shown in Table 1. Sample 1 as an embodiment of the presentinvention, and Samples 2-1 and 2-2 as comparative examples wereevaluated.

[0070] 1. Preparation of Powdery Dielectric Ceramic Raw Material

[0071] (1) Sample 1

[0072] First, BaCO₃, CaCO₃, and TiO₂ were prepared as starting materialsfor the major component ABO₃, and weighed out so that the composition of(Ba_(0.95)Ca_(0.05))TiO₃ could be produced. Subsequently, the rawmaterials were mixed for 72 hours with a ball mill and heat-treated at1150° C. Thus, (Ba_(0.95)Ca_(0.05))TiO₃ was produced. The syntheticdegree of this major component of ABO₃ was evaluated based on thecrystallographic axial ratio c/a of a tetragonal system. The axial ratioc/a was very high, i.e., 1.0101, as shown in Table 1. The average grainsize was 0.3 μm.

[0073] On the other hand, BaCO₃, CaCO₃, TiO₂, SiO₂, Dy₂O₃ and NiO wereweighed out to produce the additive component so that the respectivemolar ratio would be 1.05:0.1:1:1:0.05:0.2. Subsequently, thesematerials were mixed with a ball mill and heat-treated at 1100° C. Thus,a calcined material was obtained. The reaction made in the calcinedmaterial was identified by XRD (X-ray diffractometry). The average grainsize of the calcined material was 0.1 μm.

[0074] Next, as shown in Table 1, (Ba_(0.95)Ca_(0.05))TiO₃ and thecalcined material of Ba—Ca—Ti—Si—Dy—Ni—O were weighed out so that theamounts of Ba, Ca, Ti, Si, Dy and Ni were 1.05 moles, 0.1 mole, 1 mole,I mole, 0.1 mole, and 0.2 mole based on 100 moles of(Ba_(0.95)Ca_(0.05))TiO₃, respectively. Then, these materials were mixedwith a ball mill. Thus, a powdery raw material for the dielectricceramic of Sample 1 was produced.

[0075] (2) Sample 2-1

[0076] (Ba_(0.95)Ca_(0.05))TiO₃ as a major component ABO₃ was producedin the same manner as that for Sample 1.

[0077] To produce the additive component, BaCO₃, CaCO₃, TiO₂, SiO₂,Dy₂O₃ and NiO were weighed out so that the same composition as that ofSample 1 would be obtained. Subsequently, these materials, not calcined,were mixed with the above-described (Ba_(0.95)Ca_(0.05))TiO₃ by means ofa ball mill. Thus, a powdery raw material for the dielectric ceramic ofSample 2-1 was produced.

[0078] (3) Sample 2-2

[0079] (Ba_(0.95)Ca_(0.05))TiO₃ as a major component ABO₃ was producedin the same manner as that for Sample 1 except that the time duringwhich the BaCO₃, CaCO₃ and TiO₂ were mixed by means of the ball mill was5 hours, that is, the time was shorter compared to that for Sample 1.The synthetic degree of this major component ABO₃ was evaluated based onthe crystallographic axial ratio c/a. As shown in Table 1, the ratio waslow, i.e., 1.0084.

[0080] Subsequently, the calcined material as the additive component wasproduced in the same manner as that for Sample 1.(Ba_(0.95)Ca_(0.05))TiO₃ and the calcined material ofBa—Ca—Ti—Si—Dy—Ni—O were mixed with each other by means of a ball mill.Thus, a powdery raw material for the dielectric ceramic of Sample 2-2was produced. TABLE 1 Axial ratio c/a of Sample Major component majorcomponent Additive component number ABO₃ ABO₃ Component R Component MOthers 1 100(Ba_(0.95)Ca_(0.05))TiO₃ 1.0101 Calcined material1.05Ba—0.1Ca—1.0Ti—1.0Si—0.1Dy—0.2Ni—O * 2-1 100(Ba_(0.95)Ca_(0.05))TiO₃1.0101 0.05Dy₂O₃ 0.2NiO 1.05BaCO₃ 0.1CaCO₃ 1.0TiO₂ 1.0SiO₂ * 2-2100(Ba_(0.95)Ca_(0.05))TiO₃ 1.0084 Calcined material1.05Ba—0.1Ca—1.0Ti—1.0Si—0.1Dy—0.2Ni—O

[0081] 2. Preparation of Monolithic Ceramic Capacitor

[0082] Subsequently, a polyvinylbutyral type binder and an organicsolvent such as ethanol were added to each of the powdery raw materialsfor the dielectric ceramics of Samples 1, 2-1 and 2-2, and werewet-mixed by means of a ball mill. Thus, for each powdery raw material,ceramic slurry was produced.

[0083] Next, the ceramic slurry was formed into sheets by a doctor blademethod. The thickness of the sheets was such that the thickness of thedielectric ceramic layer after firing was 1.5 μm. Thus, rectangularceramic green sheets were produced.

[0084] Next, an electroconductive paste containing nickel as a majorcomponent was screen-printed on the ceramic green sheets. Thus, aconductive paste film to become an internal electrode was formed.

[0085] Then, plural ceramic green sheets including the ceramic greensheets having the conductive past films formed thereon were laminated insuch a manner that the sides of the ceramic green sheets to which theconductive paste films were exposed were alternately positioned on theopposite sides. Thus, a green laminate was produced.

[0086] Subsequently, the green laminate was heated at 300° C. in anitrogen atmosphere so that the binder was burned out. Thereafter, thelaminate was fired at 1200° C. for 2 hours in a reducing atmospherecontaining an H₂—N₂—H₂O gas and having an oxygen partial pressure of10⁻¹⁰ MPa. Thus, a sintered laminate was produced.

[0087] Next electroconductive paste containing B₂O₃—Li₂O—SiO₂—BaO typeglass frit and copper as an electroconductive component was applied toboth of the end faces of the laminate, and baked at 800° C. in anitrogen atmosphere. Thus, external electrodes electrically connected tothe internal electrodes were formed.

[0088] Referring to the outside sizes of the obtained monolithicceramic, the width was 1.2 mm, the length was 2.0 mm and the thicknesswas 1.0 mm. The thickness of the dielectric ceramic layer interposedbetween the internal electrodes was 1.5 μm. The number of the effectivedielectric ceramic layers was 100. The opposed area of the electrodesper layer was 1.4 mm².

[0089] 3. Analysis of Composition of Dielectric Ceramic

[0090] As regards the monolithic ceramic capacitors of Sample 1, andSamples 2-1 and 2-2, the compositions of the dielectric ceramicsconstituting the dielectric ceramic layers, respectively, were analyzedby a TEM-EDX method (Transmission Electron Microscopy-Energy DispersiveX-ray Analysis).

[0091] More specifically, the inside of a crystal grain wasplane-composition-analyzed. The areas excluding the crystal grainboundaries were image-analyzed as the insides of crystal grains. Twentycrystal grains were analyzed for determination of the composition.

[0092] The crystal grain boundaries (including triple points) wereanalyzed. In the case in which a crystal grain boundary existed as adefinite phase, the phase as the crystal grain boundary was analyzed ata probe diameter of 2 nm. As regards crystal grain boundaries which didnot exist as define phases, the analytical points between crystal grainsat which the analysis was carried out at a probe diameter of 2 nm werethe analytical points in the crystal grain boundary.

[0093] The compositions were analyzed at the analytical points in thecrystal grain boundary. In this case, the analysis of the composition inthe crystal grain boundary between two crystal grains and that in thecrystal grain boundary (triple points) among three crystal grains werecarried out at 20 randomly selected analytical points and 10 randomlyselected analytical points, respectively. TABLE 2 Ratio of number Ratioof of crystal grains Ba, Ca, Ti, Si, in which occupancy Dy, and Niexisting Sample ratio of ABO₃ is State of other in crystal grain number90% or higher crystal grains boundary  1 90% Remaining 10% 93% Occupancyratio of ABO_(3 in) crystal grain is 80% *2-1 15% Remaining 85% 33%Occupancy ratio of ABO₃ in crystal grain is 65% or lower *2-2 20%Remaining 80% 47% Occupancy ratio of ABO₃ in crystal grain is 75% orlower

[0094] Table 2 shows the composition-analytical results.

[0095] In Table 2, the expression “Ratio of number of crystal grains inwhich occupancy ratio of ABO₃ is 90% or higher” means the percentage ofthe in number of crystal grains in each of which an additive componentis not solid-dissolved, and also, the major component ABO₃ exists in 90%or higher of the area of the cross-section of the crystal grain. Forexample, the numerical value of the ratio in Table 2 is 90% in the caseof Sample 1. In particular, 18% of the 20 crystal grains analyzed hadthe additive component not solid-dissolved, and also, the majorcomponent ABO₃ exists in 90% or higher of the cross-section thereof.

[0096] In Table 2, the expression “State of other crystal grains” meansthe state of the crystal grains which are other than the above-describedcrystal grains in each of which the occupancy ratio of ABO₃ is 90% orhigher. For example, the expression “Remaining 10%” in Sample 1, meansthat the percentage of the number of crystal grains other than thecrystal grains having an occupancy ratio of 90% or higher is 10% orhigher. The expression “Occupancy ratio of ABO₃ in crystal grain is 80%”means that the percentage of the cross-section occupied by ABO₃ insidethe crystal grain is 80% or higher.

[0097] Moreover, the expression “Ratio of Ba, Ca, Ti, Si, Dy, and Niexisting in crystal Grain Boundary” in Table 2 means the ratio of thenumber of points in crystal grain boundaries at which Ba, Ca, Ti, Si, Dyand Ni can be detected. In Sample 1, for example, Ba, Ca, Ti, Si, Dy andNi were detected at analytical points equal to 93% of all the analyticalpoints in the crystal grain boundaries.

[0098]FIG. 2 shows the analytical results of the composition in crystalgrains of Sample 1, which is an embodiment of the present invention,measured by the TEM-EDX method. As seen in FIG. 2, the concentrations ofSi, Dy and Ni in Sample 1 were less than the detection lower limit (thedetection limit by the TEM analysis is 0.5 molar percent) in at least90% of the cross-sections of 90% of the number of the crystal grains.Substantially, Ba, Ca and Ti only were detected.

[0099]FIG. 3 shows the analytical results of the composition in crystalgrain boundaries of Sample 1 measured by the TEM-EDX method. As seen inFIG. 3, Ba, Ca, Ti, Si, Dy and Ni were detected in crystal grainboundaries.

[0100] On the other hand, in Samples 2-1 and 2-2, which are comparativeexamples, each crystal grain contained in the dielectric ceramic has aso-called core-shell structure comprising a shell phase in which Dy andNi are partially solid-dissolved in (Ba_(0.95)Ca_(0.05))TiO₃, and a corephase in which no additive component is solid-dissolved in(Ba_(0.95)Ca_(0.05))TiO₃.

[0101] 4. Measurement of Electrical Characteristics

[0102] Moreover, the electrical characteristics of the monolithicceramic capacitors formed with Sample 1 and Samples 2-1 and 2-2 producedas described above were determined.

[0103] The dielectric constant ε and the dielectric loss tangent (tan δ)at room temperature of each monolithic ceramic capacitor were measuredunder the conditions of a temperature of 25° C., 1 kHz and 0.5 V_(rms).

[0104] First, the ratio of the change of the electrostatic capacitancewith temperature was determined. Referring to the change ratio of theelectrostatic capacitance with temperature, the change ratios (ΔC/C₂₀)at −25° C. and at 85° C. based on the electrostatic capacitance at 20°C. were evaluated. These change ratios are Characteristic B specified inJIS (Japanese Industrial Standard). Moreover, the change ratios (ΔC/C₂₅)at −55° C. and 125° C. based on the static capacitance at 25° C. wereevaluated. These change ratios are Characteristic X7R specified in EIA(Electronic Industries Association) Standard.

[0105] Moreover, a high temperature load service life test was carriedout. According to the high temperature load service life test, a voltageof 15V is applied at a temperature of 125° C. so that the electric fieldstrength becomes 10 kV/mm. The time-dependent change of the insulationresistance is measured during the application of the voltage of 15V. Asample of which the insulation resistance becomes 200 kΩ before a lapseof 1000 hours is considered to be a rejected sample. The ratio(rejection ratio) of the number of rejected samples based on 100 samplesis determined. TABLE 3 Temperature characteristic Temperaturecharacteristic High temperature load service Sample Dielectric (ΔC/C₂₀)(%) (ΔC/C₂₅) (%) life (rejection ratio) number constant tan δ (%) −25°C. 85° C. −55° C. 125° C. 1000 hours 1 3380 7.2 −4.6 −8.5 −7.6 −11.7 0/100 * 2-1 2461 6.3 −8.1 −12.1 −11.1 −17.3 47/100 * 2-2 2352 5.4 −6.9−10.7 −9.8 −16.2 42/100

[0106] Table 3 shows the measurements of the above-described dielectricconstant ε, tan δ, the temperature characteristics (ΔC/C20 and ΔC/C25)and the rejection ratios.

[0107] As shown in Table 2, the ratio of the number of crystal grainsfor Sample 1 in each of which the occupancy ratio is about 90% or higheris more than about 85%, and the Ba, Ca, Ti, Si, Dy and Ni existing incrystal grain boundaries is 85% or higher. As seen in Table 3, althoughthe dielectric ceramic layer contained in Sample 1 has a very smallthickness of 1.5 μm, the reliability and the capacitance—temperaturecharacteristic is superior, and the dielectric ceramic has a highdielectric constant.

[0108] On the other hand, the dielectric constants are low for Samples2-1 and 2-2, which do not meet the above-described requirements, and thechange ratios of the capacitance—temperature characteristics are high,and the reliabilities are low, compared to those of Sample 1.

EXPERIMENTAL EXAMPLE 2

[0109] In Experimental Example 2, preferred ranges of the amounts of Caand Ti in dielectric ceramics according to the present invention weredetermined. The ratio Ca_(g)/Ti_(g) and the ratio Ca_(b)/Ti_(b) in whichCa_(g) and Ti_(g) represent the amounts of Ca and Ti in crystal grains,and Ca_(b) and Ti_(b) represent the amounts of Ca and Ti in crystalgrain boundaries (including a triple point), can be easily controlled bychanging the ratio of the amounts of Ca and Ti, that is, the ratioCa/Ti, in the major component raw material, and also, by changing theratio the mounts of Ca and Ti, that is, the ratio Ca/Ti, in the additivecomponent raw material.

[0110] Table 4 for Experimental Example 2 corresponds to Table 1 forExperimental Example 1. Table 4 shows the compositions and thecrystallographic axial ratios c/a of the major components ABO₃ and thecompositions of calcined materials formed as the additive components insamples prepared in Experimental Example 2. TABLE 4 Crystallo- graphicSam- axial ratio ple c/a of major num- Major component componentAdditive component ber ABO₃ ABO₃ (calcined material) 3100(Ba_(0.95)Ca_(0.05))TiO₃ 1.01021.1Ba—0.2Ca—1.0Ti—1.4Si—1.0Dy—1.0Mn—0.5Ni—0.5Mg—O 4100(Ba_(0.90)Ca_(0.10))TiO₃ 1.01011.05Ba—0.1Ca—0.8Ti—0.8Si—1.2Er—1.0Mn—O 5100(Ba_(0.90)Ca_(0.10))(Ti_(0.995)Zr_(0.005))O₃ 1.00970.95Ba—0.15Ca—1.0Ti—1.2Si—1.2Er—1.0Co—0.5Cr—O 6100(Ba_(0.97)Ca_(0.03))(Ti_(0.985)Zr_(0.005)Hf_(0.01))O₃ 1.00981.1Ba—0.25Ca—0.8Ti—1.0Si—0.5Y—0.5Ho—0.8Mg—O 7100(Ba_(0.97)Ca_(0.03))(Ti_(0.99)Zr_(0.01))O₃ 1.00921.0Ba—0.05Ca—1.0Ti—1.4Si—0.8Y—0.3Tm—1.0Mg—0.2Fe—O 8100(Ba_(0.95)Ca_(0.05))(Ti_(0.995)Hf_(0.005))O₃ 1.00971.05Ba—0.05Ca—1.5Ti—1.0Si—0.5Sm—0.5Ho—0.8Mn—0.4Fe—O 9100(Ba_(0.90)Ca_(0.08)Sr_(0.02))O₃ 1.00980.95Ba—0.1Ca—2.0Ti—0.8Si—1.2Yb—0.5Cu—0.3Mn—0.2Ni—O 10100(Ba_(0.90)Ca_(0.08)Sr_(0.02))(Ti_(0.99)Zr_(0.01))O₃ 1.00901.1Ba—0.1Ca—1.5Ti—0.5Si—1.0Y—0.4Yb—0.5Mn—0.5Al—O

[0111] Monolithic ceramic capacitors were prepared in a manner similarto that in Experimental Example 1, using the respective samples shown inTable 4. The electrical characteristics were evaluated similarly tothose of Experimental Example 1. Table 5 shows the evaluation results ofthe electrical characteristics. As regards the high temperature loadservice life test, the test for the 1000 hour service life was carriedout similarly to that in Experimental Example 1, and in addition, a 2000hour test was conducted.

[0112] Table 5 also shows the ratio Ca_(g)/Ti_(g) in crystal grainscontained in the dielectric ceramic constituting a dielectric ceramiclayer of the produced monolithic ceramic capacitor and the ratioCa_(b)/Ti_(b) in crystal grain boundaries contained in the dielectricceramic. TABLE 5 Temperature Temperature High temperature characteristiccharacteristic load service life Sample Ratio Ratio Dielectric (ΔC/C₂₀)(%) (ΔC/C₂₅) (%) (rejection ratio) number Ca_(g)/Ti_(g) Ca_(b)/Ti_(b)constant tan δ (%) −25° C. 85° C. −55° C. 125° C. 1000 hours 2000 hours3 0.052 0.179 3275 6.3 −3.0 −8.0 −5.2 −11.0 0/100 0/100 4 0.099 0.1212886 8.4 −2.4 −7.5 −4.7 −10.2 0/100 0/100 5 0.100 0.144 2892 8.1 −2.3−7.4 −4.8 −10.3 0/100 0/100 6 0.041 0.311 3420 5.1 −2.1 −7.8 −5.7 −12.20/100 0/100 7 0.029 0.052 3624 5.3 −3.8 −9.5 −6.2 −14.1 0/100 0/100 80.053 0.034 3423 6.4 −3.2 −8.7 −5.8 −11.8 0/100 9/100 9 0.084 0.046 31087.9 −2.9 −8.3 −5.5 −11.7 0/100 34/100  10 0.090 0.068 3055 7.9 −2.6 −8.0−5.1 −11.3 0/100 16/100 

[0113] The ratio Ca_(b)/Ti_(b) is made larger than the ratioCa_(g)/Ti_(g) in Samples 3 to 7 as shown in Table 5, by employing aratio Ca/Ti of the additive component raw material which is higher thanthe ratio Ca/Ti of the major component raw material as shown in Table 4.On the other hand, the ratio Ca_(b)/Ti_(b) for Samples 8 to 10 is madesmaller than the ratio Ca_(g)/Ti_(g) as shown in Table 5, by employingthe ratio Ca/Ti in the major component raw material which is higher thanthe ratio Ca/Ti in the additive component raw material.

[0114] Samples 3 to 10 show superior electrical characteristics as shownin Table 5. Especially in the 2000 hour high-temperature load servicelife (rejection ratio), Samples 3 to 7 of which the ratio Ca_(b)/Ti_(b)is larger than the ratio Ca_(g)/Ti_(g), respectively, exhibit a higherreliability than Samples 8 to 10 of which the ratio Ca_(b)/Ti_(b) issmaller than the ratio Ca_(g)/Ti_(g), respectively.

EXPERIMENTAL EXAMPLE 3

[0115] Experimental Example 3 was carried out to evaluate a preferredrange of the concentration of Ca in crystal grains contained in thedielectric ceramic.

[0116] Table 6 corresponds to Table 1 for Experimental Example 1. Table6 shows the compositions and the crystallographic axial ratio c/a of themajor components ABO₃ and the compositions of the calcined materialsformed as the additive components in samples prepared in ExperimentalExample 3. TABLE 6 Crystallographic axial ratio c/a of Sample Majorcomponent manor component Additive component number ABO₃ ABO₃ (calcinedmaterial) *11  100BaTiO₃ 1.00991.1Ba—0.2Ca—1.0Ti—1.4Si—1.0Dy—1.0Mn—0.5Ni—0.5Mg—O 12100(Ba_(0.99)Ca_(0.01))TiO₃ 1.01021.1Ba—0.2Ca—1.0Ti—1.4Si—1.0Dy—1.0Mn—0.5Ni—0.5Mg—O 13100(Ba_(0.89)Ca_(0.10)Sr_(0.01))TiO₃ 1.00971.0Ba—0.1Ca—1.2Ti—1.2Si—1.0Dy—1.0Mn—0.5Ni—0.5Mg—O 14100(Ba_(0.80)Ca_(0.20))(Ti_(0.995)Hf_(0.005))O₃ 1.00951.0Ba—0.1Ca—1.2Ti—1.2Si—1.0Dy—1.0Mn—0.5Ni—0.5Mg—O 15100(Ba_(0.79)Ca_(0.21))TiO₃ 1.00941.0Ba—0.2Ca—1.0Ti—1.4Si—1.0Dy—1.0Mn—0.5Ni—0.5Mg—O

[0117] As shown in Table 6, powdery dielectric ceramic raw materialswere prepared which contained the major components ABO₃ in which theamounts of Ca substituted for the sites A in the major components ABO₃were different, that is, the Ca substitution amounts were different.Monolithic ceramic capacitors were prepared in the same manner as thatemployed in Experimental Example 1. For the produced monolithic ceramiccapacitors, the electrical characteristics were evaluated similarly tothose in Experimental Example 2. Table 7 shows the evaluation results.TABLE 7 Temperature Temperature High temperature characteristiccharacteristic load service life Sample Dielectric (ΔC/C₂₀) (%) (ΔC/C₂₅)(%) (rejection ratio) number constant tan δ (%) −25° C. 85° C. −55° C.125° C. 1000 hours 2000 hours * 11 2314 1 −9.8 −2.2 −16.3 −20.4 0/1000/100 12 3290 3.5 −2.8 −9.2 −6.8 −14.3 0/100 0/100 13 3208 6.6 −2.4 −4.3−4.2 −7.2 0/100 0/100 14 2987 8.5 −0.9 −3.1 −2.0 −2.8 0/100 0/100 152686 9.1 −0.8 −2.9 −1.2 −3.1 7/100 33/100 

[0118] As shown in Table 6, no Ca is added to the major component ABO₃in Sample 11. As a result, example 11 has a low dielectric constant andan inferior capacitance—temperature characteristic compared to the otherSamples 12 to 15 as shown in Table 7.

[0119] In the case of Samples 12 to 15, Ca is added to the majorcomponents ABO₃ thereof, as shown in Table 6. As a result, Samples 12 to15 show superior electrical characteristics, as shown in Table 7.

[0120] Samples 12 to 15 were compared with each other. In Samples 12 to14, the Ca concentrations of the major component ABO₃ are in the rangeof about 1 to 20 molar percent. In Sample 15, the Ca concentration is 21molar percent, i.e., exceeds about 20 molar percent. As a result,Samples 12 to 14 of which the Ca concentrations are in the range ofabout 1 to 20 molar percent exhibit higher dielectric constants andhigher reliabilities (rejection ratio) in the high temperature loadservice life test, compared to Sample 15 of which the Ca concentrationdeparts from the range of 1 to 20 molar percent.

EXPERIMENTAL EXAMPLE 4

[0121] Experimental Example 4 was carried out to evaluate a preferredrange of the addition amount based on 100 moles of the major componentABO₃ of an additive component raw material R (at least one of La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y), and a preferredrange of the addition amount on a compound basis, on 100 moles of themajor component ABO₃ of an additive component raw material M (at leastone of Mn, Ni, Cu, Fe, Cr, Cu, Mg, Al, V, Mo and W).

[0122] Table 8 corresponds to Table 1 for Experimental Example 1, andshows the compositions and the crystallographic axial ratios c/a of themajor components ABO₃, and the compositions of the calcined materialsformed as the additive components in the samples prepared inExperimental Example 4. Moreover, the concentrations by mole ratio,based on 100 moles of the major component, on an element basis of theabove-described components R and M are shown in the lower part of eachcolumn of “Additive component (calcined material)”. TABLE 8 Crystallo-graphic axial ratio c/a Sam- of major ple com- num- Major componentponent Additive component (calcined material) ber ABO₃ ABO₃ Component R(mole) Component M (mole) *19  100(Ba_(0.90)Ca_(0.10))TiO₃ 1.00980.95Ba—0.1Ca—0.8Ti—1.4Si—0.6Mn—0.2Ni—0.2Mg—0.1V—O 0 1.1 20100(Ba_(0.90)Ca_(0.10))TiO₃ 1.00980.95Ba—0.1Ca—0.8Ti—1.4Si—0.04Yb—0.02La—0.02Gd—0.6Mn—0.2Ni—0.5V—0.2Al—O0.08 1.3 21 100(Ba_(0.93)Ca_(0.05)Sr_(0.02))TiO₃ 1.00960.95Ba—0.1Ca—0.8Ti—1.4Si—0.4Dy—0.2Sm—0.2Ho—0.5Mg—0.3Cr—O 0.8 0.8 22100(Ba_(0.90)Ca_(0.04)Sr_(0.01))TiO₃ 1.00930.95Ba—0.1Ca—0.8Ti—1.4Si—0.6Dy—0.3Eu—0.3Er—0.6Mn—0.5Ni—0.5Cr—O 1.2 1.623 100(Ba_(0.90)Ca_(0.10))TiO₃ 1.01010.95Ba—0.1Ca—1.2Ti—1.8Si—1.0Dy—0.5Ce—0.2Tm—1.0Mn—0.5Ni—0.5Mg—O 1.7 2*24  100(Ba_(0.97)Ca_(0.03))(Ti_(0.995)Zr_(0.005))O₃ 1.00961.0Ba—0.1Ca—1.2Ti—1.8Si—0.5Sm—0.5Ho—O 1 0 25100(Ba_(0.97)Ca_(0.03))(Ti_(0.995)Zr_(0.005))O₃ 1.00971.0Ba—0.1Ca—1.2Ti—1.8Si—0.5Sm—0.5Ho—0.2Pr—0.06Mn—0.02Mo—0.02W—O 1.2 0.1226 100(Ba_(0.97)Ca_(0.02)Sr_(0.01))TiO₃ 1.00941.0Ba—0.1Ca—1.2Ti—1.8Si—0.5Yb—0.5Ce—0.5Tb—0.4Mn—0.2Mg—0.2Cu—O 1.5 0.8 27100(Ba_(0.97)Ca_(0.03))(Ti_(0.99)Hf_(0.01))O₃ 1.00971.0Ba—0.1Ca—1.2Ti—1.8Si—0.4Y—0.3Nd—0.1Lu—1.0Mn—0.6Co—0.4Fe—O 0.8 2 28100(Ba_(0.96)Ca_(0.03)Sr_(0.01))TiO₃ 1.00981.0Ba—0.1Ca—1.2Ti—1.8Si—0.5Y—0.4Gd—0.2Eu—1.0Mn—0.5Ni—0.5Fe—0.2Al—O 1.12.2

[0123] As shown in Table 8, the amounts of the components R contained inthe additive components in Samples 19 to 23 are increased as the samplenumber becomes larger. Moreover, the addition amounts of the component Min the additive components are increased in Samples 24 to 28 as thesample number becomes larger.

[0124] Table 9 shows the electrical characteristics of monolithicceramic capacitors produced using the powder dielectric ceramic rawmaterials having the compositions shown in Table 8, in the same manneras that in Experimental Example 1. The items of the electricalcharacteristics evaluated and shown in Table 9 are the same as those inExperimental Example 2. TABLE 9 Temperature Temperature High temperaturecharacteristic characteristic load service life Sample Dielectric(ΔC/C₂₀) (%) (ΔC/C₂₅) (%) (rejection ratio) number constant tan δ (%)−25° C. 85° C. −55° C. 125° C. 1000 hours 2000 hours * 19 3598 8.5 −2.4−0.1 −5.3 −19.6 43/100  98/100  20 3221 8.7 −2.4 −7.7 −4.2 −10.1 0/1000/100 21 3162 6.8 −2.5 −7.6 −4.9 −10.4 0/100 0/100 22 3145 7.1 −3.1 −9.0−4.8 −12.2 0/100 0/100 23 2686 5.3 −2.7 −9.2 −4.8 −12.5 0/100 0/100 * 243562 8.1 −2.9 −1.2 −5.3 −18.0 73/100  100/100  25 3485 5.7 −3.2 −8.2−5.1 −11.7 0/100 0/100 26 3420 5.6 −3.5 −8.2 −4.9 −12.1 0/100 0/100 273212 5.8 −2.8 −9.4 −5.0 −13.8 0/100 0/100 28 2640 5.5 −3.3 −9.5 −5.2−14.1 0/100 0/100

[0125] Samples 19 to 23 were compared with each other. First, thecomponent R is not added to the additive component in Sample 19.Accordingly, as seen in Table 9, Sample 19 exhibits a low reliability,as evaluated by the high temperature load service life test, and isinferior in the capacitance—temperature characteristic (ΔC/C₂₅) comparedto the other samples. On the other hand, Samples 20 to 23 exhibit a highreliability, as evaluated by the high temperature load service lifetest, and a superior evaluation result with regard to the temperaturecharacteristic.

[0126] Samples 20 to 23 were compared with each other. In Samples 20 to22, the concentration of the component R meets the requirement that theconcentration of the component R should be in the range of about 0.05 to1.5 mole based on 100 moles of the major component. The samples 20 to 22exhibit a higher dielectric constant and a superior temperaturecharacteristic compared to Sample 23 of which the concentration of thecomponent R exceeds about 1.5 moles.

[0127] Samples 24 to 28 were compared with each other. the component Mis not added to the additive component in Sample 24. Thus, theinsulating property can not be ensured for Sample 24. Moreover, thereliability evaluated by the high temperature load service life test islow. Furthermore, the temperature characteristic (ΔC/C₂₅) is inferiorcompared with the other samples. On the other hand, Samples 25 to 28exhibit superior results obtained by the high temperature load servicelife test and the temperature characteristic test.

[0128] Samples 25 to 28 were compared with each other. Samples 25 to 27in which the concentrations of the components M of the additivecomponents are in the range of about 0. I to 2 moles based on 100 molesof the major component exhibit a higher dielectric constant and asuperior temperature characteristic compared to Sample 28 of which theconcentration of the component M exceeds about 2 moles.

What is claimed is:
 1. A dielectric ceramic having crystal grains andcrystal grain boundaries between the crystal grains comprising: aperovskite compound having the general formula ABO₃, as a majorcomponent, in which A represents Ba and Ca, or Ba, Ca and Sr, and Brepresents Ti, or Ti and at least one of Zr and Hf, and an additivecomponent containing Si, R and M, in which R represents at least one ofLa, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, and Mrepresents at least one of Mn, Ni, Co, Fe, Cr, Cu, Mg, Al, V, Mo and W,wherein the additive component is not solid-dissolved and, wherein themajor component exists in at least about 90% of the cross-section of atleast about 85% by number of all of the crystal grains, and wherein atleast Ba, Ca, Ti, Si, R and the M are found at about 85% or more of theanalytical points in the crystal grain boundaries.
 2. A dielectricceramic according to claim 1, wherein Ca_(g)/Ti_(g) <Ca_(b)/Ti_(b), inwhich Ca_(g) is the amount of Ca, and Ti_(g) is the amount of Ticontained in the crystal grains, and Ca_(b) is the amount of Ca, andTi_(b) is the amount of Ti contained in the crystal grain boundaries. 3.A dielectric ceramic according to claim 2, wherein the concentration ofCa in the crystal grains is in the range of about 1 to 20 molar percentbased on the amount of the element A in the major component ABO₃.
 4. Adielectric ceramic according to claim 3, wherein the concentrations onan element basis of the R and the M in the additive component are in theranges of about 0.05 to 1.5 moles and about 0.1 to 2 moles,respectively, based on 100 moles of the major component.
 5. A dielectricceramic according to claim 4, wherein the perovskite has acrystallographic axial ratio c/a of at least about 1.009.
 6. Adielectric ceramic according to claim 1, wherein the concentration of Cain the crystal grains is in the range of about 1 to 20 molar percentbased on the amount of the element A in the major component ABO₃.
 7. Adielectric ceramic according to claim 1, wherein the concentrations onan element basis of the R and the M in the additive component are in theranges of about 0.05 to 1.5 moles and about 0.1 to 2 moles,respectively, based on 100 moles of the major component.
 8. A dielectricceramic according to claim 1, wherein the perovskite has acrystallographic axial ratio c/a of at least about 1.009.
 9. A method ofproducing a dielectric ceramic comprising the steps of: providing amixture of (a) a perovskite compound having the general formula ABO₃ inwhich A represents Ba and Ca, or Ba, Ca and Sr, and B represents Ti, orTi and at least one of Zr and Hf, the perovskite compound having acrystallographic axial ratio c/a of at least about 1.009 and (b) acalcined material containing at least Ba, Ca, Ti, Si, R and M, in whichR is at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,Lu and Y, and M is at least one of Mn, Ni, Co, Fe, Cr, Cu, Mg, Al, V, Moand W; and firing the mixture of the perovskite compound and thecalcined material.
 10. A method of producing a dielectric ceramicaccording to claim 9, wherein the mole ratio Ca/Ti of the perovskitecompound is smaller than the mole ratio Ca/Ti in the calcined material.11. A method of producing a dielectric ceramic according to claim 10,wherein the concentrations on an element basis of the R and the M in thecalcined material are in the ranges of about 0.05 to 1.5 moles and about0.1 to 2 moles, respectively, based on 100 moles of the perovskite. 12.A monolithic ceramic capacitor comprising a laminate which comprises atleast three laminated dielectric ceramic layers and at least twointernal electrodes extended along different interfaces betweendielectric ceramic layers and overlapping each other in the laminationdirection; and a pair of external electrodes on outer surfaces of thelaminate so as to be electrically connected to different internalelectrodes; wherein the dielectric ceramic layers comprise thedielectric ceramic of claim
 5. 13. A monolithic ceramic capacitoraccording to claim 12, wherein the internal electrodes comprise a basemetal.
 14. A monolithic ceramic capacitor according to claim 13, whereinthe base metal comprises nickel or copper.
 15. A monolithic ceramiccapacitor according to claim 14, wherein the external electrodescomprise a base metal.
 16. A monolithic ceramic capacitor according toclaim 13, wherein the external electrodes comprise a base metal.
 17. Amonolithic ceramic capacitor comprising a laminate which comprises atleast three laminated dielectric ceramic layers and at least twointernal electrodes extended along different interfaces betweendielectric ceramic layers and overlapping each other in the laminationdirection; and a pair of external electrodes on outer surfaces of thelaminate so as to be electrically connected to different internalelectrodes; wherein the dielectric ceramic layers comprise thedielectric ceramic of claim
 1. 18. A monolithic ceramic capacitoraccording to claim 17, wherein the internal electrodes comprise a basemetal.
 19. A monolithic ceramic capacitor according to claim 18, whereinthe base metal comprises nickel or copper.
 20. A monolithic ceramiccapacitor comprising a laminate which comprises at least three laminateddielectric ceramic layers and at least two internal electrodes extendedalong different interfaces between dielectric ceramic layers andoverlapping each other in the lamination direction; and a pair ofexternal electrodes on outer surfaces of the laminate so as to beelectrically connected to different internal electrodes; wherein thedielectric ceramic layers comprise the dielectric ceramic of claim 4.